LM4549 AC ’97 Rev 2.1 Codec with Sample Rate Conversion and National 3D Sound
February 1999
LM4549
AC ’97 Rev 2.1 Codec with Sample Rate Conversion and
National 3D Sound
General Description
The LM4549 is an audio codec for PC systems which is fully
PC98 compliant and performs the analog intensive functions
of the AC97 Rev2.1 architecture. Using 18-bit Sigma-Delta
A/D’s and D/A’s, the LM4549 provides 90dB of Dynamic
Range.
The LM4549 was designed specifically to provide a high
quality audio path and provide all analog functionality in a PC
audio system. It features full duplex stereo A/D’s and D/A’s
and an analog mixer with 4 stereo and 3 mono inputs, each
of which has separate gain, attenuation and mute control.
The codec features a second Line Output known as True
Line Level Out that is identical to Line Out but with indepen-
dent volume control. The LM4549 also features National’s
3D Sound stereo enhancement and variable sample rate
conversion. The sample rate for the A/D and D/A can be pro-
grammed separately with a resolution of 1Hz to convert any
rate between 4kHz-48kHz.
The AC97 architecture separates the analog and digital func-
tions of the PC audio system allowing both for system design
flexibility and increased performance.
Key Specifications
n
Analog Mixer Dynamic Range
n
D/A Dynamic Range
n
A/D Dynamic Range
97dB (typ)
89dB (typ)
90dB (typ)
Features
n
AC’97 Rev 2.1 compliant
n
National’s 3D Sound circuitry
n
High quality Sample Rate Conversion (SRC) from 4kHz
to 48kHz in 1Hz increments.
n
Multiple Codec Support
n
External Amplifier Power Down (EAPD) control from
codec
n
PC-Beep passthrough to Line Out while reset is held
active low
n
True Line Level Output with volume control independent
of Line Out
n
Digital 3V and 5V compliant
Applications
n
Desktop PC Audio Systems on PCI cards, AMR cards,
or with motherboard chips sets featuring AC-Link
n
Portable PC Systems as on MDC cards, or with a
chipset or accelerator featuring AC-Link
Block Diagram
DS101035-1
FIGURE 1. LM4549 Block Diagram
© 1999 National Semiconductor Corporation
DS101035
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
